Purpose
To avoid having to enter the following code to achieve the proper link and italics:
Code: {{Pattern|Ket|battlecruiser}}
Result: Ket-pattern battlecruiser
Usage
Most cases we want to provide a direct link to the article with the minimum of fuss.
Code: {{Pattern|Ket|battlecruiser}}
Result: Ket-pattern battlecruiser
Sometimes, we don't want to use the ship's type as the follow on text.
Code: {{Class|CCS|battlecruiser|ship}}
Result: CCS-class ship
If we want to leave out the follow-on text altogether, we make the third parameter empty.
Code: {{Pattern|Ket|battlecruiser|}} and the text that comes after.
Result: Ket-pattern and the text that comes after.